Method and apparatus for receiving a control channel

ABSTRACT

Various methods and apparatuses for receiving a control channel involve a communication device monitoring a first control and receiving information from a network regarding the configuration of a second control channel. The communication device receives an uplink grant from the network; transmits a message to the network, in which the message indicates to the network that the communication device is capable of monitoring the second control channel. The communication device monitors the second control channel based on the configuration information receiving via the first control channel.

CROSS-REFERENCE

The present application is a continuation of U.S. patent applicationSer. No. 13/566,381, filed on Aug. 3, 2012, the disclosure of which isincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to wireless communication, andmore particularly to monitoring control channels in such systems.

BACKGROUND

In wireless communication systems, especially mobile communicationnetworks, control signaling is often necessary to support downlink datachannels. Control signaling enables a device in a network tosuccessfully receive, demodulate, and decode the downlink signals itreceives. For example, in Long-Term Evolution (LTE) networks, thePhysical Downlink Control Channel (PDCCH) and (for LTE Release 11 andbeyond) the Enhanced Physical Downlink Control Channel (EPDCCH) are usedfor control signaling. The PDCCH and/or EPDCCH provides a device or UserEquipment (UE) with information that allows the device to, for example,process data that is downloaded/transmitted from the network (via one ormore base stations) over the Physical Data Shared Channel (PDSCH). TheUEs in an LTE network typically do not “know” exactly where thePDCCH/EPDCCH control channels are located in the downlink framesreceived from the network, and must therefore search the frames tolocate the appropriate control channels. Such searching is oftenchallenging.

It may be the case that some UEs in LTE networks are capable ofreceiving an EPDCCH while other are not. Such a mismatch can introducecomplications. Furthermore, some cells of an LTE network may be capableof using an EPDCCH while others are not. This may introduce morecomplications when a UE is handed over from one cell that isEPDCCH-capable to one that is not (or vice versa).

The various aspects, features and advantages of the invention willbecome more fully apparent in the following description with theaccompanying drawings described below. The drawings may have beensimplified for clarity and are not necessarily drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example of a communication system in which variousembodiments of the invention may be implemented.

FIG. 2 shows a block diagram depicting certain aspects of a TP inaccordance with an embodiment of the invention.

FIG. 3 shows a block diagram depicting aspects of a device that that mayfunction as a UE in an embodiment of the invention.

FIG. 4 depicts a sub-frame according to an embodiment of the invention.

FIG. 5 shows an example of how the TP of FIG. 1 creates and transmits aUE-specific control channel in an embodiment of the invention.

FIGS. 6-11 depict various techniques for a UE to receive one or more ofa PDCCH and EPDCCH under various conditions according to variousembodiments of the invention.

In accordance with the foregoing, methods and apparatuses for receivinga control channel will now be described.

According to an embodiment of the invention, a method involves acommunication device monitoring a first control channel (e.g., a firsttype of control channel, such as a PDCCH) and receiving information froma network regarding the configuration of a second control channel (e.g.,a second type of control channel, such as an EPDCCH). The method furthercomprises receiving an uplink grant from the network; transmitting amessage to the network, in which the message indicates to the networkthat the communication device is capable of monitoring the secondcontrol channel (e.g., the EPDCCH); and monitoring the second controlchannel based on the received configuration information of the secondcontrol channel. In an embodiment of the invention, the communicationdevice receives the uplink grant and transmits the capability messageduring a random access procedure (e.g., during a RACH procedurereceiving the uplink grant as part of a msg2 and transmitting thecapability message as part of a new msg3, respectively).

In an embodiment of the invention, the communication device receives atransmission from a network (e.g., receiving one or more of asynchronisation signal, a broadcast channel, a Master Information Block,and a System Information Block). Based on the transmission (e.g., basedon the synchronisation signal structure (e.g., synchronization sequence,position of the synchronization sequence within a subframe and/ortime-frequency resources used, synchronization signal bandwidth, type ofsynchronization signal, etc.), information received in the broadcastchannel, the Master Information Block, and/or the System InformationBlock identifying whether the network is Release 11 capable or not), thecommunication uses either a first or a second default transmission mode(e.g., the communication device uses the default transmission mode basedon the type of network—tm9 if the network is Release 11 capable; tm1 or2 if not) to receive data from the network (e.g., the PDSCH).

According to an embodiment, a communication device transmits a messageto a network via a random access channel (e.g., msg1 via RACH). Inresponse to the transmission, the communication device receives anidentifier (e.g. TC-RNTI). The communication device determines whetherthe identifier falls into a recognized range. If the identifier fallswithin the recognized range, responding to the receipt of the identifierwith a message indicating that the communication device is capable ofmonitoring a control channel (e.g., if the identifier falls within arange that the device recognizes as signifying that the network isEPDCCH capable, the device informs the network that it is also EPDCCHcapable).

In an embodiment of the invention, the communication device receives amessage indicating that the communication device is to ceasecommunicating with the first cell and begin communicating with thesecond cell (e.g., a handover message). The handover message includesone or more of: time-frequency resources of a control channel of thesecond cell (e.g., which PRBs that the device is to monitor for theEPDCCH), which antenna ports the device is to use to communicate via thecontrol channel (e.g., which antenna ports does the device use tomonitor for the EPDCCH), and energy per resource element information ofthe second cell (e.g., information that the device can use to determinethe EPRE of the REs on which it receives the EPDCCH—e.g., ratio ofEPDCCH EPRE to UE-specific RS EPRE within each OFDM symbol containingUE-specific RS, ratio of EPDCCH EPRE to cell-specific RS EPRE among foreach OFDM symbol containing an EPDCCH).

The various embodiments disclosed herein are frequently described in thecontext of an LTE cellular system. It is to be understood, however, thatthe scope of the invention is not limited to LTE and may be implementedin other types of wireless networks (IEEE 802.11, 802.16, etc.).

The various embodiments disclosed herein are frequently described in thecontext of an Long Term Evolution (LTE) cellular system. It is to beunderstood, however, that the scope of the invention is not limited toLTE and may be implemented in other types of wireless networks (IEEE802.11, 802.16, etc.).

Prior to proceeding with this disclosure, a couple of preliminaryconcepts will now be described in accordance with certain embodiments ofthe invention. A list of acronyms is provided at the end of thisdisclosure to facilitate reading.

A “channel” according to an embodiment of the invention refers to one ormore paths over which to transmit information. This includes a logicalchannel, a transport channel, and a physical channel. As used herein,“channel” may refer to a logical channel. When describing embodiments ofthe invention in the LTE context herein, “channel” refers to a transportchannel, which is characterized by how data is transferred over theradio interface, including the channel coding scheme, the modulationscheme, antenna mapping, etc. However, when used in conjunction with“physical” in this disclosure, “channel” refers to a physical channel,which, in the LTE context, corresponds to a set of physical resources(e.g. time-frequency and/or resources, etc) that carry information fromhigher layers. Each physical channel may or may not have a correspondingtransport channel. When used in the context of a Channel StateInformation (CSI) or Channel Quality information (CQI) or channelestimation or multipath fading channel, the term “channel” refers to thewireless propagation channel between the UE and the TP or between the TPand the UE.

An “antenna port” according to an embodiment of the invention may be alogical port that may correspond to a beam (resulting from beamforming)or may correspond to a physical antenna at a UE or a TP. An antenna portmay be defined such that a channel over which a symbol on the antennaport is conveyed can be inferred from the effective channel over whichanother symbol on the same antenna port is conveyed. More generally, anantenna port can correspond to any well-defined description of atransmission from one or more of antennas. As an example, it couldinclude a beamformed transmission from a set of antennas withappropriate antenna weights being applied, where the set of antennasitself could be unknown to a UE. In some particular implementations“antenna port” can also refer to a physical antenna port at the TP. Incertain cases, the beamforming or precoding applied at the TP may betransparent to the UE. In other words, the UE need not know whatprecoding weights are used by the TP for a particular transmission onthe downlink. Typically, a transmission associated with an antenna portmay include transmission of pilots (or reference signals associated withthe antenna port) so that the receiving device can use the pilots toperform channel estimation and equalization and subsequent receivedsignal processing e.g. to recover the transmitted information.

A “layer” in an embodiment of the invention describes the relationshipamong the various protocols and communication technologies used in, forexample, LTE as well as the relationship between those protocols and thephysical signaling. While there are many ways to conceptualize theserelationships, a common method, which will be used herein, is to referto three layers: Layer 1, also known as the physical layer; Layer 2,also known as the Media Access Control (MAC) layer; and Layer 3, alsoknown as the Radio Resource Control (RRC) layer. Layers 2 and 3 areoften referred to as the “higher layers.” Layer 1 refers to thosetechnologies that enable the physical transmission of radio channels,and the raw bits or symbols contained therein. Layer 2, which isgenerally considered to be split into two sublayers: the MAC layer andthe Packet Data Convergence Protocol (PDCP) layer. In general, Layer 2refers to those technologies that enable functions such as mappingbetween transparent and logical channels, error correction throughHybrid Automatic Repeat Request (HARQ) priority handling and dynamicscheduling, and logical channel prioritization. Layer 3 handles the mainservice connection protocols, such as the Non-Access Stratum (NAS)protocol and the RRC protocol. It is to be understood, however, thatdifferent conceptualizations of these various technologies is possible,and that the layers may be organized differently.

The previously-mentioned use of the term “layer” is not to be confusedwith “spatial layer,” which refers to spatial multiplexing and theability of, for example, multiple antennas to multiplex differentsignals in different geometrical positions and orientations.

A “Radio Network Temporary Identifier” (RNTI) is an identifier used forcommunication between the between the eNB and the UE. In LTE, there areseveral types of RNTI, including C-RNTI (Cell RNTI), RA RNTI (RandomAccess Response RNTI), SI-RNTI (System Information RNTI), SPS C-RNTI(Semi persistent scheduling C-RNTI), Temporary C-RNTI, and Paging RNTI(P-RNTI). Some RNTIs may be UE-specific (i.e. assigned on a UE basis,e.f. C-RNTI, SPS C-RNTI), while some RNTIs are cell-common (e.g. such asP-RNTI, SI-RNTI, etc). Some RNTIs are fixed by specification (e.g.SI-RNTI, etc) and some may be explicitly or implicitly assigned. Eachseparate physical channel may have its own RNTI. For instance, thecell-specific broadcast PDCCH scheduling the system information and theassociated physical data shared channel (PDSCH) use the SI-RNTI.Similarly, UE-specific PDCCH scheduling UE-specific information and theassociated physical data shared channel (PDSCH) may use the C-RNTI.Typically the RNTIs are used as part of the scrambling sequenceinitializations for the associated physical channels and/or as part ofthe downlink control information message (e.g. CRC masking operations).

An example of a network in which an embodiment of the invention operateswill now be described. FIG. 1 illustrates a communication system 100,which includes a network 102. The network 102 includes, TPs 103, 104 and105 (which may be implemented as eNBs or Remote Radio Heads (RRHs)), anduser equipment (UE) or communication device 106, 107 and 108. Variouscommunication devices may exchange data or information through thenetwork 102. The network 102 may be an evolved universal terrestrialradio access (E-UTRA) or other type of telecommunication network. Forone embodiment, a TP may be a distributed set of servers in the network102. In another embodiment, a TP may correspond to a set ofgeographically collocated or proximal physical antenna elements. A UEmay be one of several types of handheld or mobile devices, such as, amobile phone, a laptop, or a personal digital assistant (PDA). In oneembodiment, the UE may be a wireless local area network capable device,a wireless wide area network capable device, or any other wirelessdevice. A TP may have one or more transmitters and one or morereceivers. The number of transmitters at a TP may be related, forexample, to the number of transmit antennas at the TP. Similarly, a UEmay have multiple receive antennas communicating with one or more of theTPs. Each antenna port may carry signals to a UE from a TP and from theTP to the UE. Each antenna port may also receive these signals. In oneembodiment, the network 100 is capable of using Coordinated Multipoint(COMP) techniques.

FIG. 2 illustrates a possible configuration of a TP (e.g., one or moreof the TPs in FIG. 1). The TP may include a processor/controller 210, amemory 220, a database interface 230, a transceiver 240, input/output(I/O) device interface 250, and a network interface 260, connectedthrough bus 270. The TP may implement any operating system, such asMicrosoft Windows®, UNIX, or LINUX, for example. Client and serversoftware may be written in any programming language, such as C, C++,Java or Visual Basic, for example. The server software may run on anapplication framework, such as, for example, a Java® server or .NET®framework.

The processor/processor 210 may be any programmable processor. Thesubject of the disclosure may also be implemented on a general-purposeor a special purpose computer, a programmed microprocessor ormicroprocessor, peripheral integrated circuit elements, anapplication-specific integrated circuit or other integrated circuits,hardware/electronic logic circuits, such as a discrete element circuit,a programmable logic device, such as a programmable logic array, fieldprogrammable gate-array, or the like. In general, any device or devicescapable of implementing the decision support method as described hereinmay be used to implement the decision support system functions of thisdisclosure.

The memory 220 may include volatile and nonvolatile data storage,including one or more electrical, magnetic or optical memories such as arandom access memory (RAM), cache, hard drive, or other memory device.The memory may have a cache to speed access to specific data. The memory220 may also be connected to a compact disc-read only memory (CD-ROM),digital video disc—read only memory (DVD-ROM), DVD read write input,tape drive, or other removable memory device that allows media contentto be directly uploaded into the system. Data may be stored in thememory 220 or in a separate database. The database interface 230 may beused by the processor/controller 210 to access the database. Thedatabase may contain any formatting data to connect UE to the network102 (FIG. 1). The transceiver 240 may create a data connection with theUE.

The I/O device interface 250 may be connected to one or more inputdevices that may include a keyboard, mouse, pen-operated touch screen ormonitor, voice-recognition device, or any other device that acceptsinput. The I/O device interface 250 may also be connected to one or moreoutput devices, such as a monitor, printer, disk drive, speakers, or anyother device provided to output data. The I/O device interface 250 mayreceive a data task or connection criteria from a network administrator.

The network connection interface 260 may be connected to a communicationdevice, modem, network interface card, a transceiver, or any otherdevice capable of transmitting and receiving signals from the network106. The network connection interface 260 may be used to connect aclient device to a network. The network connection interface 260 may beused to connect the teleconference device to the network connecting theuser to other users in the teleconference. The components of the TP maybe connected via an electrical bus 270, for example, or linkedwirelessly.

Client software and databases may be accessed by the processor/processor210 from memory 220, and may include, for example, databaseapplications, word processing applications, as well as components thatembody the decision support functionality of the present disclosure. ATP (FIG. 1) may implement any operating system, such as MicrosoftWindows®, LINUX, or UNIX, for example. Client and server software may bewritten in any programming language, such as C, C++, Java or VisualBasic, for example. Although not required, the disclosure is described,at least in part, in the general context of computer-executableinstructions, such as program modules, being executed by the electronicdevice, such as a general purpose computer. Generally, program modulesinclude routine programs, objects, components, data structures, etc.that perform particular tasks or implement particular abstract datatypes. Other embodiments may be practiced in network computingenvironments with many types of computer system configurations,including personal computers, handheld devices, multi-processor systems,microprocessor-based or programmable consumer electronics, network PCs,minicomputers, mainframe computers, and the like.

FIG. 3 illustrates in a block diagram one embodiment of atelecommunication apparatus or electronic device to act as a UE (such asone or more of the UEs depicted in FIG. 1). The UE may be capable ofaccessing the information or data stored in the network 102. For someembodiments of the disclosure, the UE may also support one or moreapplications for performing various communications with the network 102.

The UE may include a transceiver 302, which is capable of sending andreceiving data over the network 102. The UE may include a processor 304that executes stored programs. The UE may also include a volatile memory306 and a non-volatile memory 308 which are used by the processor 304.The UE may include a user input interface 310 that may comprise elementssuch as a keypad, display, touch screen, and the like. The UE may alsoinclude a user output device that may comprise a display screen and anaudio interface 312 that may comprise elements such as a microphone,earphone, and speaker. The UE also may include a component interface 314to which additional elements may be attached, for example, a universalserial bus (USB) interface. Finally, the UE may include a power supply316.

It is to be noted that various embodiments of the inventive methodsdescribed herein may be carried out on the hardware described withreference to FIG. 3 or FIG. 4, or in some cases both. It is to beunderstood that there may be many other components of a UE, TP, network,or communication system that are known in the art but not depicted inthis disclosure, but that would be used in conjunction with theembodiments described in this disclosure.

Referring back to FIG. 1, one or more of the TPs and one or more the UEsmay include one or more transmitters and one or more receivers. Thenumber of transmitters may be related, for example, to the number oftransmit antennas at the TP and UE. The TP and the UE may also havemultiple antennas. A multiple antenna configuration on either a TP or aUE is generally supports MIMO communication.

Referring again to FIG. 1, the general mode of communication of thesystem 100 according to an embodiment of the invention will now bedescribed. Although the communication will often be referred to astaking place between the network 102 and a UE 106, it is to beunderstood that this is for ease of description, and that thecommunication takes place between one or more of the TPs of the network102 and the UE 106.

The network 102 and the UE 106 generally communicate via physical ULchannels and physical DL channels. The physical medium used for thecommunication is Radio Frequency (RF) signals. The RF signals aretransmitted on a carrier frequency with a predefined channel bandwidth.The modulation scheme used for communication between the network 102 andthe UE 106 differs depending on whether the signals are being sent inthe UL direction (travelling from the UE 106 to network 102) or the DLdirection (travelling from the network 102 to the UE 106). Themodulation scheme used in the DL direction is a multiple-access versionof OFDM called Orthogonal Frequency-Division Multiple Access (OFDMA). Inthe UL direction, Single Carrier Frequency Division Multiple Access(SC-FDMA) is used.

According to an embodiment of the invention, orthogonal subcarrierstransmitted in the DL direction are modulated with a digital stream,which may include data, control information, or other information, so asto form a set of OFDM symbols. The subcarriers may be contiguous ordiscontiguous. DL data modulation may be performed using quadraturephase shift-keying (QPSK), 16-ary quadrature amplitude modulation(16QAM), or 64QAM, although other modulation schemes may be used. TheOFDM symbols are configured into a DL sub-frame. Each OFDM symbol has atime duration and is associated with a cyclic prefix (CP). A CP issimilar to a guard period between successive OFDM symbols in asub-frame, but its primary function is to render the data transmitted ondifferent subcarriers orthogonal upon application of a Fast FourierTransform (FFT) in a receiver in a multipath fading channel.

The DL data carried by the OFDM signals is organized into radio frames.Each radio frame typically includes ten sub-frames. An example of thestructure of a sub-frame is shown in FIG. 4, which depicts a sub-frame400 represented as a time-frequency diagram. A vertical scale of thediagram depicts multiple blocks of frequency, also referred to asfrequency bins or frequency subcarriers. A horizontal scale of thediagram depicts multiple blocks of time (in units of OFDM symbols) ofthe sub-frame 400 that may be allocated. The sub-frame 400 comprisesmultiple resource blocks (RBs) such as Resource Block 0 (RB0), ResourceBlock 1 (RB1), Resource Block 2 (RB2), and Resource Block 3 (RB3).Typically, each RB comprises 12 OFDM subcarriers over a time slotcomprising 7 OFDM symbols. Typically, the sub-frame duration is 1 ms andis organized into two time slots of 0.5 ms duration each. Each RB can bedivided into multiple resource elements (REs). Each RE is a single OFDMsubcarrier, or frequency bin, on a single OFDM symbol. It is to be notedthat many frames and sub-frames may be transmitted from the network 104to the UE 106 and vice-versa, and that various channels may occupy slotsin many sub-frames.

The sub-frame 400 may also be used to carry other signals and channelssuch as synchronization signals such as Primary/SecondarySynchronization channels (P/S-SCH), broadcast control channels,including primary broadcast control channel (PBCH), etc. The PBCHincludes the MIB. The MIB includes a portion of a system frame number(SFN), downlink system bandwidth, Physical Hybrid ARQ Channel (PHICH)configuration (such as duration and PHICH resource indicator), PDCCH andEPDCCH related (e.g., indication) configuration information (describedin more detail elsewhere).

To enable DL communication to occur smoothly, the network 102 usescontrol signaling, including DL signaling via DL control channels. Onesuch DL control channel is the Physical Downlink Common Control Channel(PDCCH) which is located at the start of each DL sub-frame (up to thefirst three OFDM symbols). Another is the Enhanced Physical DownlinkControl Channel (EPDCCH) which is located on one or more RB-pairsspanning both slots in the sub-frame. Each of these channels carries theDL scheduling assignment, UL scheduling grants, UL transmit powercontrol commands, etc. In one embodiment, EPDCCH is used in LTE Release11, and is an enhanced version of the PDCCH, which is used in LTEReleases 8, 9, and 10.

Each of the PDCCH and EPDCCH carries Downlink Control Information (DCI).DCI provides the UE with information necessary for proper reception anddecoding of downlink data. DCI may include DL information such asscheduling assignments, including PDSCH resource indication, transportformat, hybrid ARQ information, and spatial multiplexing controlinformation. DCI may also include UL scheduling grants and ULinformation of the same types as the DL information.

The network 102 (FIG. 1) transmits the PDCCH to the UE 106 in a set ofRBs that span the entire frequency range of the sub-frame 400. Incontrast, the EPDCCH may be transmitted over only a portion of thefrequency range. In the sub-frame 400 of FIG. 4, for example, the UE 106receives the EPDCCH in RB0 and RB1, i.e., RB-pairs spanning both slotsof the sub-frame, but only part of its frequency range.

Another example of a downlink channel that can be carried in thesub-frame 400 is the physical downlink shared channel (PDSCH). The PDSCHis used to send user data and control information (such as pagingmessages) to all mobile devices operating within its coverage area.

To decode information carried on the PDCCH in an embodiment of theinvention, the UE carries out channel estimation. To perform channelestimation, UE uses Reference Signals (RS) or pilot symbols that itreceives in the sub-frame 400. The reference signals are associated withone or more antenna ports. For example, a UE using LTE Release 8, 9, or10 uses the reference signals associated with one or more of antennaports 0, 1, 2, and 3. The RS structure for antenna ports 0, 1, 2, and 3is shown in FIG. 4, in which R0, R1, R2, R3 are resource elementscarrying reference signals associated with antenna ports 0, 1, 2, and 3respectively.

To decode data carried on the PDSCH in an embodiment of the invention,the UE 106 may use RS received in the sub-frame 400. For example, a UEusing LTE Release 10 the UE can either use reference symbols associatedwith one or more of antenna ports 0, 1, 2, or 3, or use referencesymbols associated with one or more of antenna ports 7, 8, 9, 10, 11,12, 13, 14. The selection of antenna ports to be used is based on thetransmission mode used for PDSCH reception. The concept of a“transmission mode” is described in more detail elsewhere. A referencesignal associated with antenna ports 7-14 are typically referred to as a“UE specific reference signal (UERS)” or “Demodulation reference signal(DMRS).” A reference signal associated with antenna ports 0,1,2,3 istypically referred to as “Cell-specific Reference Signal (CRS).” While aCRS is sent across the entire carrier bandwidth by the TP, the DMRS mayonly be present in those RBs for which the UE has a PDSCH assignment.

Another type of reference signal that may be included in the sub-frame400 is a Channel State Information Reference Signal (CSI-RS). The CSI-RSis used by the UE to determine channel-state information (CSI) that theUE reports to the network 102. In one embodiment, the CSI includes aChannel Quality Indicator (CQI). The CQI gives the network 102information about the link adaptation parameters that the UE can supportat that time, taking into account the transmission mode, the receivertype of the UE, the number of antennas being used by the UE, and theinterference being experienced by the UE. In one embodiment, the CQI isdefined by a sixteen entry table with Modulation and Coding Schemes(MCS).

In an embodiment of the invention, a PDCCH is transmitted on one or anan aggregation of consecutive Control Channel Elements (CCEs). In aPDCCH, a CCE has 9 Resource Element Groups (REGs), with each REGcontaining 4 Resource Elements (REs), for a total of 36 REs.

In an embodiment of the invention, an EPDCCH is transmitted on one or anaggregation of enhanced control channel elements (eCCEs). An eCCE cancorrespond to a set of REs in a set of resource blocks on which EPDCCHis transmitted. The set of REs that correspond to an eCCE may be furthergrouped into enhanced resource element groups (eREGs). The size of aneCCE may not be fixed, and may correspond to different number of REs indifferent subframes.

In an embodiment of the invention, each instance of a PDCCH or EPDCCHhas its own configuration. The configuration of a PDCCH or EPDCCH isindicated by a PDCCH or EPDCCH configuration message respectively. A“configuration” in this context is described by a set of “attributes.”Possible attributes of a PDCCH or EPDCCH include: CCE size (or eCCEsize), CCE aggregation level (or eCCE aggregation level), localizedtransmission of the CCEs (or eCCEs), distributed transmission of theCCEs (or eCCEs), its transmission scheme, its SNR gain, the set of RBsin which it is contained, the antenna ports it uses, the number ofantenna ports it uses, the number of spatial layers it uses, thescrambling sequence for its (EPDCCH or PDCCH) coded bits, initializationor portion of the initialization or parameters for computing theinitialization of the scrambling sequence generator for the scramblingsequence for PDCCH or EPDCCH coded bits, UERS or DMRS sequence or DMRSscrambling sequence, initialization or portion of the initializationparameters for computing the initialization (e.g, DMRS scramblingsequence identifier) of the scrambling sequence generator for DMRSsequence, DMRS signature sequence (sequence used to modulate the DMRSsequence), its modulation, and the PDCCH or EPDCCH to reference signal(e.g., DMRS) power boost ratio, which is determined, for example, fromthe ratio of the Energy Per Resource Element (EPRE) of the PDCCH orEPDCCH to that of the reference signal (e.g., DMRS).

An example of two EPDCCHs having configurations that differ in one ormore attributes is as follows: EPDCCH configuration #1 has 4 eCCEs, DMRSport #7, RBs {#5, #20, #35, #45}, 0 dB power boost. EPDCCH configuration#2 has 8 eCCEs, DMRS port #7, RBs {#5, #20, #35, #45}, 3 dB power boost.Thus, the two configurations differ in 2 attributes: # of eCCEs andpower boost.

To receive the PDCCH or the EPDCCH in accordance with an embodiment ofthe invention, a UE monitors a set of PDCCH or EPDCCH candidates (e.g.,candidate RBs). In this context, “monitoring” refers to the UEattempting to decode each of the candidates in the PDCCH or EPDCCHcandidate set according to all applicable DCI formats for thatcandidate. The set of EPDCCH or PDCCH candidates to be monitored by UE,that is, the EPDCCH or PDCCH candidate set, can also be defined in termsof search spaces. The EPDCCH or PDCCH candidates that UE monitors mayinclude a set of Common Search Space (CSS) candidates, and a set of UESpecific Search Space (UESS) candidates. The UESS corresponding toEPDCCH may optionally be called an enhanced UESS (eUESS). CSS candidatesare monitored by all UEs in a cell, while UESS candidates are specificto individual UEs and are monitored by the UEs for which they areintended.

When monitoring the CSS, a UE starts decoding from a CCE or eCCE withknown logical index (e.g. CCE0). This restriction further simplifies thecommon search. The UE attempts to decode every possible PDCCH or EPDCCHcandidate set for given PDCCH or EPDCCH format until it successfullydecodes the PDCCH or EPDCCH that is present in the CSS.

To optimize the searching process in an embodiment of the invention,CCEs (eCCEs) may be aggregated into groups, or “aggregations,” which aresearched together. The sizes of the aggregations (i.e., how many CCEs oreCCEs are therein) are classified into “aggregation levels.” Forexample, an search space S_(k) ^((L)) at aggregation level L can referto a set of candidates in which each candidate in the search space has Laggregated CCEs (or eCCEs). A PDCCH may have aggregations of 1, 2, 4,and 8 CCEs, with each CCE including 36 REs. An EPDCCH may also haveaggregations of 1, 2, 4, and 8 CCEs (or eCCEs). However, since the sizeof the CCEs (or eCCEs) of an EPDCCH is not fixed, other aggregationlevels (e.g. L=3 or L=12) may be used. Also, since the size of theEPDCCH CCEs (or eCCEs) can change considerably between differentsub-frames and slots within a sub-frame (for example, based on controlregion size, presence of CSI-RS, and sub-frame type), a set ofaggregation levels that the UE 106 assumes for EPDCCH monitoring alsomay vary between sub-frames or between slots in a same sub-frame orbetween different sub-frame types (for example, a normal sub-frame vs.an MBSFN sub-frame). More generally, a set of aggregation levels thatthe UE assumes for EPDCCH monitoring can vary between over time.

An example of how the TP 104 (FIG. 1) creates and transmits aUE-specific EPDCCH or PDCCH and how the UE 106 extracts the EPDCCH orPDCCH intended for the UE 106 will now be described with reference toFIGS. 1 and 4, and to FIG. 5. For the sake of simplicity, this examplewill be described in the context of EPDCCH, though it is to beunderstood that the process may be the same for a PDCCH.

Preliminarily, the UE 106 performs a random access to the network 102using a Random Access Channel (RACH) (FIG. 5). In doing so, the UE 106transmits a RACH preamble sequence, referred to as msg1, to the TP 104.The UE 106 receives a RACH response, referred to here as msg2, from theTP 106. The msg2 contains an identifier called a Temporary C-RNTI(TC-RNTI). The UE 106 transmits a msg3 to the network 102, whichidentifies the UE 106 to the network 102. Specifically, the UE 106 usesa pre-existing C-RNTI or another pre-existing identifier to identifyitself. If the UE 106 has been previously identified to the network 102,then the UE 106 already has a C-RNTI, and uses that C-RNTI to identifyitself. Otherwise, the UE 106 uses another pre-existing identifier suchas S-TMSI (S-Temporary Mobile Subscriber Identity). After transmittingmsg3, the UE 106 uses the TC-RNTI (or C-RNTI) to monitor the PDCCH foruplink grants and downlink assignments. Once the UE receives a messageindicating successful contention resolution—a msg4—it promotes itsTC-RNTI to a C-RNTI if it does not already have a C-RNTI. The UE thencontinues monitoring the UESS using the C-RNTI.

Once the TP 104 and UE 106 have completed the RACH process, the TP 104creates an EPDCCH message. To do so, the TP 104 determines theappropriate EPDCCH format, creates the appropriate DCI and attaches aCRC. The CRC is then masked with an RNTI. Which RNTI is used depends ofthe purpose for with the EPDCCH is to be used. If, for example, theEPDCCH is for a specific UE, the CRC will be masked with the C-RNTI ofthe specific UE. Other RNTIs may be used in other scenarios.

To obtain the control information from the EPDCCH, the UE 106 carriesout blind decoding. In other words, the UE 106 monitors a set of EPDCCHcandidates (a set of consecutive CCEs (or eCCEs) on which EPDCCH couldbe mapped) in every sub-frame. The UE 106 de-masks each EPDCCHcandidate's CRC using the C-RNTI. If no CRC error is detected, the UE106 considers it as a successful decoding attempt and reads the controlinformation within the successful EPDCCH candidate.

It is to be noted that there are possible variations on the aboveprocedure. For example, if the EPDCCH contains paging information, theCRC may be masked with a paging indication identifier, i.e., P-RNTI. Ifthe EPDCCH contains system information, a system information identifier,i.e., a SI-RNTI, may be used to mask the CRC.

In accordance with an embodiment of the invention, in order to receivethe PDSCH, a UE may be configured with a transmission mode from amongmultiple known transmission modes. During initial access to the network,that is, before receiving transmission mode configuration signaling fromthe network 102, the UE 106 can receive the PDSCH by assuming a defaultvalue for transmission mode. In LTE Releases 8, 9, and 10, the defaultvalues for transmission mode are tm1 for a one CRS antenna port systemand tm2 for a two CRS antenna port system. In LTE Release 11, thedefault value for transmission mode is tm9. The network 102 cansubsequently configure the UE with other non-default values fortransmission modes to receive PDSCH. The aspect of UE receiving PDSCHusing a default value for transmission mode is also referred to asreceiving PDSCH using a “default transmission mode”.

According to various embodiments, each transmission mode has certainattributes. For example, if the UE is configured with transmission mode2, the UE can receive the PDSCH using CRS and a transmit diversitytransmission scheme. If the UE is configured with transmission modes 3,4, 5, or 6, the UE can receive the PDSCH using CRS and Multiple InputMultiple Output (MIMO) based transmission schemes such as open loopspatial multiplexing, closed loop spatial multiplexing and Multi-UserMIMO (MU-MIMO). If the UE is configured with transmission modes 7 or 8,the UE can receive the PDSCH using UE-specific RSs. If the UE isconfigured with transmission mode 9, the UE can receive the PDSCH usingDMRS, and spatial multiplexing of up to eight spatial layers ispossible. Transmission mode 9 is suitable for PDSCH reception usingfeatures such as CoMP and MIMO techniques such as MU-MIMO. Configuringthe UE in transmission mode 9 also allows for beamformedfrequency-selective transmission of the PDSCH to the UE.

In an embodiment of the invention, in order to provide the required databandwidth, several carriers may be used together in a process calledcarrier aggregation (CA). Using this processes several carriers areaggregated on the physical layer to provide the required bandwidth. Toan a UE that is not capable of using CA terminal, each component carrierappears as a separate carrier, while a UE that is CA-capable can exploitthe total aggregated bandwidth of the multiple carriers as if they werea single carrier.

When carrier aggregation is employed, at least one of the TPs acts asthe “primary cell” or Pcell, and the other TPs act as secondary cells orScells. The Pcell is often referred to as the “anchor cell,” and itscarrier is often referred to as the “anchor carrier”. The Pcell is thecell that operates on the primary frequency, to which the UE (1)performs an initial connection establishment procedure, (2) initiatesthe connection re-establishment procedure, or (3) is indicated as theprimary cell in a handover procedure. The Scell, on the other hand, is acell that operates on a secondary frequency, which may be configuredonce an RRC connection is established.

In an embodiment of the invention a type of Scell is New Carrier Type(NCT). An NCT does not transmit one or more of a CRS, a PSS, an SSS, orpaging signals.

According to an embodiment of the invention, one or more of the UEs mayemploy the technique of Discontinuous Reception (DRX). This techniqueallows a terminal to put its frequency modem into a sleep state for longperiods, activating it only in well defined, suitable, instants. Thiskeeps the terminal from having to continuously monitor control channels.

EPDCCH UESS Monitoring

Referring to FIG. 6, one scheme for EPDCCH based UESS monitoring willnow be described. In this embodiment, the network configures the UE tomonitor for the EPDCCH by transmitting EPDCCH configuration informationto the UE via the PDCCH. For example, the UE may monitor the UESS forthe PDCCH. The UE eventually identifies and successfully decodes thePDCCH meant for it. Over the PDCCH, the network sends, for example, DLassignments scrambled via TC-RNTI to the UE. The network may also usethe PDCCH to send higher layer (MAC/RRC) messages to the UE, such asmessages requesting UE capability, messages that indicate the RBs/RBpairs on which the UE is to monitor for the UESS-based EPDCCH (i.e.,EPDCCH based UESS candidates or eUESS candidates), and messages thatconfigure the UE to monitor for the UESS-based EPDCCH.

In an embodiment of the invention, the network may also change thetransmission mode of the UE from one transmission mode to another usingthe same RRC message that the network uses to configure the UE tomonitor for the UESS-based EPDCCH. For example, in LTE, EPDCCH and PDSCHboth use a DMRS-based transmission mode. In some implementations of LTE,transmission mode 9 allows both PDSCH and EPDCCH to be received at thesame time using different DMRS antenna ports. The network could send amessage to the UE to configure it to use transmission mode 9 and amessage that configures the UE to monitor for the EPDCCH in a single RRCmessage

In a more specific example, if the network supports both Release 8/9/10UEs and Release 11 UEs, the network can reuse the same initial setupsignaling for both types of UEs. After the network receives UEcapability/category information from the UEs, the network canindividually configure Release 11 UEs for EPDDCH UESS monitoring.

In some embodiments, the network 102 does not know whether a UE 106 isEPDCCH-capable (e.g., whether the UE is a Release 11 UE). In oneimplementation, the UE 106 first determines a ‘default’ EPDCCHconfiguration. The UE then informs the network that it is EPDCCH-capableduring a RACH procedure as follows: The UE transmits a RACH preamblesequence (msg1) to the network. In response, it receives a RACH response(msg2) and the RACH response contains TC-RNTI. The UE uses the TC-RNTI(or C-RNTI, as explained elsewhere) to identify itself in its subsequentUL transmissions (and to scramble its UL transmissions). The UEtransmits what will be referred to as ‘new msg3’ to the network. The newmsg3 includes a unique identifier that is associated with the UE (e.g. aTMSI). The new msg3 also includes bits or information that indicate tothe network that the UE is capable of supporting EPDCCH reception.

Some possible bits that the UE may use to inform the network that the UEis EPDCCH-capable are as follows: (1) The UE can use bit(s) in a“criticalExtensionsFuture” field in a “RRCConnectionRequest” message ofthe new msg3 to indicate to the network that it is capable of supportingEPDCCH reception. (2) The UE can use a spare bit in a“RRCConnectionRequest-r8-IEs” information element in a“RRCConnectionRequest” message of the new msg3 to indicate to thenetwork that it is capable of supporting EPDCCH reception. (3) The UEcan use spare bit(s) in a “EstablishmentCause” information element in a“RRCConnectionRequest” message of the new msg3 to indicate to thenetwork that it is capable of supporting EPDCCH reception.

It should be noted that the embodiments described previously may varywith respect to the order in which functions are carried out and whichactions are “cause” and which are “effect.” For example, when a UEtransmits a preamble sequence as part of a RACH procedure, the TPreceiving the preamble may be an Scell, while the UL grant may betransmitted to the UE by the Pcell. Thus, the “response” to the preamblesequency may be made by a TP other than the “recipient” of the preamblesequence.

After transmitting the new msg3, the UE starts monitoring EPDCCH usingthe default EPDCCH configuration. By virtue of the information in thenew msg3, the network now knows that the UE is EPDCCH-capable andtherefore can begin to send UE-specific EPDCCH control signals using thedefault EPDCCH configuration.

The default EPDCCH configuration can include information identifying aset of PRB-pairs (Physical resource block pairs) on which the UEmonitors EPDCCH. The set of PRB-pairs is usually smaller than thetransmission bandwidth configuration of the carrier on which EPDCCH ismonitored. For example, if the transmission bandwidth configuration of acarrier is 100 RBs (this corresponds to 20 MHz carrier or channelbandwidth, each RB can logically correspond to a PRB-pair), the defaultEPDCCH configuration can include information identifying a set of 4RB-pairs within the 100 RBs. The default EPDCCH configuration can alsoinclude information identifying a set of antenna ports based on whichthe UE can receive EPDCCH. The default EPDCCH configuration can alsoinclude information using which the UE can determine the EPRE (energyper resource element) of the REs (resource elements) on which itreceives EPDCCH.

The default EPDCCH configuration is determined by the UE based on asignal from the network. The signal from the network can include one ormultiple bits of information transmitted by a TP in the network. Thebits may be transmitted as part of the MIB or one of the SIBs. SIBs arereceived by the UE on PDSCH RBs assigned via CSS PDCCHs whose CRC isscrambled with SI-RNTI. In one implementation, the signal from thenetwork is a message (included in MIB or SIBs) that explicitly indicatesthe default EPDCCH configuration to the UE. In another implementation,the UE may implicitly determine the default EPDCCH configuration using asignal from the network. For example the UE may determine the defaultEPDCCH configuration using a cell identifier (or a transmission pointID) of an eNB (or a transmission point) in the network. For example, theUE may use network signals such as PSS (Primary synchronization signal),SSS (secondary synchronization signal), CRS (cell-specific referencesignal) or CSI-RS (CSI reference signal or Channel state informationreference signal) to determine an identifier associated with an eNB or atransmission point of the network. For example, the identifier can be aPCID (Physical cell identifier) or a TP-ID (transmission pointidentifier). The UE can then use the identifier to implicitly determinethe default EPDCCH configuration to receive EPDCCH.

The default EPDCCH configuration can correspond to a set of PRB pairs onwhich the UE monitors EPDCCH candidates that are transmitted using adistributed mapping format. When EPDCCH is transmitted using distributedmapping, each CCE (or eCCE) of the monitored EPDCCH candidate is mappedto more than on PRB-pair.

After the UE starts monitoring UESS-based EPDCCH candidates using thedefault EPDCCH configuration, it may receive higher layer signalingconfiguring it to monitor EPDCCH candidates using an additional EPDCCHconfiguration. After receiving such signaling, the UE may monitor EPDCCHcandidates based on both the default EPDCCH configuration and theadditional EPDCCH configuration. The additional EPDCCH configuration canbe signaled to the UE using RRC signaling in a dedicated RRC message(e.g. a “RRCConnectionReconfiguration” message that includes a“radioResourceConfigDedicated” field). The additional EPDCCHconfiguration can include information identifying additional sets ofPRB-pairs and antenna ports to monitor EPDCCH. The sets of PRB-pairsidentified in the default EPDCCH configuration and the additional EPDCCHconfiguration can overlap.

For receiving PDSCH, an EPDCCH-capable UE can use the same CRS-basedtransmission mode as non-EPDCCH capable UEs. For example, a Release 11UE can use the same CRS-based default transmission modes that Release 8,9, and 10 UEs use for receiving SIBs and RACH responses (i.e., tm1 forthe 1 CRS antenna port case and tm2 for the 2 CRS antenna port case).However, after transmitting the new msg3 the UE can receive PDSCH usinga new default transmission mode that allows it to receive PDSCH usingDMRS (e.g. tm9). This is because when the network receives the new msg3,it will know the UE is EPDCCH capable (e.g., is a Release 11 UE), andcan begin sending the PDSCH to the UE using tm9.

FIG. 7 shows an example implementation of these features. As shown, theUE monitors CSS using PDCCH. The UE also receives a default EPDCCHconfiguration from the network using one of the above-described methods.After transmitting the new msg3 the UE starts monitoring EPDCCH UESSusing the default EPDCCH configuration. Similarly, after receiving themsg3, the network sends UESS-based EPDCCH information to the UE. If theUE is not configured with a C-RNTI, the UE initially monitors EPDCCHUESS using a Temporary C-RNTI (TC-RNTI) and after contention resolutionis successful, it promotes the TC-RNTI to a C-RNTI and monitors EPDCCHUESS using C-RNTI. Also, the UE can receive additional EPDCCHconfiguration from higher layers (e.g. RRC) to monitor additional EPDCCHUESS candidates using C-RNTI.

According to another embodiment, the eNB may not always be able toschedule using EPDCCH in response to the new msg3. For example, (a) theeNB may want to use a different EPDCCH configuration than the defaultconfiguration, (b) the eNB may not want to use EPDCCH for thisparticular UE (e.g., it may be a delay tolerant “Machine type” UE(typically engaged in Machine Type Communications) and the eNB prefersto use EPDCCH capacity for conventional UEs), or (c) the eNB may nothave enough EPDCCH capacity. In such cases, the eNB would need toschedule the UE using PDCCH. In order to enable this, the UE can beconfigured to monitor for both PDCCH and EPDCCH after transmitting msg3.If the first transmission from the eNB to the UE is via EPDCCH, the UEswitches to an EPDCCH-only mode; if the first transmission from the eNBto the UE is via PDCCH, the UE switches to a PDCCH only mode. During theperiod when the UE is monitoring both EPDCCH and PDCCH candidates, theUE's blind decodes are split between PDCCH and EPDCCH (i.e., not allaggregation levels can be used for either PDCCH or EPDCCH). Once the UEswitches to EPDCCH-only mode or PDCCH-only mode, all the blind decodescan be used towards EPDCCH or PDCCH respectively.

In some implementations, the UE receives a signal from the network,based on the received signal, can determine which transmission mode touse to receive the PDSCH. If the nature and content of the signalindicate that the network is not an EPDCCH-capable network, then the UEmay choose to receive PDSCH using a first default transmission mode(i.e., receive PDSCH using a first default value for transmission mode).If the signal indicates that the network is not an EPDCCH-capablenetwork, then the UE may choose to receive the PDSCH in a second defaulttransmission mode (i.e., receive PDSCH using a second default value fortransmission mode). For example, if the signal indicates that thenetwork is an LTE Release 8/9/10 network, then the UE may adopt aRelease 8/9/10 default transmission mode—tm1 or tm2—in which the PDSCHis received based on CRS. If, on the other hand, the signal indicatesthat the network is an LTE Release 11 (or other future release) network,then the UE may adopt a Release 11 default transmission mode—tm9—inwhich the PDSCH is received based on DMRS. The UE can receive PDSCHusing the second default transmission mode until it receives a higherlayer message configuring the UE to receive PDSCH using a differenttransmission mode (i.e., a configured transmission mode rather than adefault transmission mode).

The signal from the network can include one or multiple bits ofinformation transmitted by an eNB in the network. The bits may betransmitted as part of MIB or one of the SIBs. In one implementation,the signal from the network is a message (included in MIB or SIBs) thatexplicitly indicates parameters relevant for receiving PDSCH using thesecond default transmission mode. For example, the parameters caninclude DMRS antenna ports based on which PDSCH is received in thesecond default transmission mode, and/or, information indicating zeropower CSI-RS RE locations based on which the UE determines the REs usedfor receiving PDSCH in the second default transmission mode, and/or,information indicating non-zero power CSI-RS RE locations based on whichthe UE determines the REs used for receiving PDSCH in the second defaulttransmission mode. Alternately, the signal from the network may be oneor more of PSS (Primary synchronization signal), SSS (secondarysynchronization signal), CRS (cell-specific reference signal) or CSI-RS(CSI reference signal or Channel state information reference signal). Inone implementation, if UE determines from the Synchronization Signalsthat it is operating on a first carrier type (e.g. a type that supportsonly EPDCCH), it will use tm9 as the default value of transmission modefor receiving PDSCH. Otherwise, if it determines from theSynchronization Signals that it is operating on a legacy carrier type(e.g. a type that supports only PDCCH or both PDCCH and EPDCCH), it willuse tm1/tm2 as the default value for tm.

In an embodiment, illustrated in FIG. 8, if control and balancing ofload between PDCCH and EPDCCH is necessary, then the temporary C-RNTIcan be used to control when UEs will indicate that they are EPDCCHcapable. In this implementation (1) The network reserves a C-RNTI rangeto be used for EPDCCH capable UEs. This range can be advertised insystem information or can be fixed in a commonly understoodspecification. The network subsequently determines a need to scheduleincoming EPDCCH capable UEs using EPDCCH. (2) The UE transmits a RACHpreamble as part of a connection establishment procedure. (3) If thereis available EPDCCH capacity, the TP responds with an RACH responseincluding an UL grant and a TC-RNTI from the C-RNTI range for EPDCCHcapable UEs. (3)(a) A Rel 11 EPDCCH capable UE recognizes the TC-RNTI asbelonging to range. The UE transmits a new msg3. (3)(b) A UE not capableof EPDCCH (including legacy UEs) transmits a legacy msg 3. (4) If the TPreceives a new msg3, it schedules a msg4 and subsequent transmissions tothe UE using EPDCCH. Otherwise the TP uses PDCCH. If contentionresolution succeeds, the UE uses the TC-RNTI of step 3 as the C-RNTI. Itshould be noted that the reserved C-RNTI range is not exclusive toEPDCCH capable UEs. That is, all EPDCCH capable UEs receive TC-RNTIsfrom the reserved C-RNTI range, but non-EPDCCH capable UEs may alsoreceive TC-RNTIs from this range.

In some embodiments, the resource allocation (e.g. location of the PRBswithin the transmission bandwidth configuration of a carrier) in thescheduling grant for the RACH response (msg2) can be used to implicitlyindicate whether EPDCCH or PDCCH or a combination of EPDCCH and PDCCH(on the same or different subframes) is to be used or supported for aRel-11 or later UE. A UE not capable of EPDCCH (including legacy UEs)would monitor only PDCCH. Alternatively, the resource allocation (e.g.location of the PRBs) for the msg3 uplink transmission can indicatewhether EPDCCH or PDCCH or a combination of EPDCCH and PDCCH (on thesame or different subframes) is to be used for a Rel-11 or later UE.

In one embodiment of the invention, the CSS is monitored for the PDCCHonly in sub-frames not configured as MBSFN sub-frames (e.g., sub-frames0, 4, 5, or 9). In such a scenario, the number of EPDCCH UESS blinddecoding candidates in MBSFN sub-frames can be increased. For example,in subframes configured as MBSFN subframes the UE may perform blinddecoding for 44 EPDCCH candidates (e.g 8 candidates at aggregation level1, 8 candidates at aggregation level 2, 3 candidates at aggregationlevel 4 and 3 candidates at aggregation level 8 for two different DCIformat sizes), in subframes not configured as MBSFN subframes, the UEmay perform blind decoding for 32 EPDCCH candidates (e.g 6 candidates ataggregation level 1, 6 candidates at aggregation level 2, 2 candidatesat aggregation level 4 and 2 candidates at aggregation level 8 for twodifferent DCI format sizes).

EPDCCH Monitoring—Handover Scenarios

When a UE gets handed over from one serving cell to a different servingcell (e.g. based on the handover message(s)), the EPDCCH configurationmay be included in a handover message.

FIG. 9 shows an example. The UE monitors CSS using PDCCH. To determinethe mapping of PDCCH REs the UE uses a first cell ID. The UE alsomonitors UESS using EPDCCH. The UE may determine the mapping of EPDCCHREs using a previously determined EPDCCH configuration (e.g., based on adefault EPDCCH configuration and/or additional EPDCCH configurationsignaled by the network). The UE receives a handover message orderingthe UE to handover from the first cell to a second cell. In someimplementations, a handover message is a “RRCConnectionReconfiguration”message including a “mobilityControlInfo” information element. Afterreceiving the handover message, the UE continues to monitor a CSS usingPDCCH. However, to determine the mapping of PDCCH REs, the UE uses asecond cell ID (cell ID of the second cell). After receiving thehandover message, the UE also continues to monitor a UESS using EPDCCH.However, to determine the mapping of EPDCCH REs, the UE uses informationin the handover message.

In one implementation (as shown in FIG. 9), the information in thehandover message is a new EPDCCH configuration that is received in thehandover message. The new EPDCCH configuration can include informationidentifying a set of PRB-pairs (Physical resource block pairs) of thesecond cell that the UE monitors for the EPDCCH. The set of PRB-pairs isusually smaller than the transmission bandwidth configuration of thecarrier associated with the second cell. For example, if thetransmission bandwidth configuration of the carrier is 100 RBs (thiscorresponds to 20 MHz carrier bandwidth, each RB can logicallycorrespond to a PRB-pair), the new EPDCCH configuration can includeinformation identifying a set of 4 RB-pairs within the 100 RBs. The newEPDCCH configuration can also include information identifying a set ofantenna ports based on which the UE can receive EPDCCH in the secondcell. The new EPDCCH configuration can also include information usingwhich the UE can determine the EPRE (energy per resource element) of theREs (resource elements) on which it receives EPDCCH of the second cell.

In another implementation, the handover message can include anidentifier associated with the second cell (e.g. PCID of second cell).The UE can implicitly determine a set of PRB-pairs of the second cell(for EPDCCH monitoring) based on the identifier. The UE may alsoimplicitly determine a set of antenna ports of the second cell (forEPDCCH monitoring) based on the identifier associated with the secondcell. Alternately, the UE may use the same antenna ports that were usedfor EPDCCH monitoring in the first cell.

In some implementations, if a new EPDCCH configuration is not receivedin the handover message, the UE continues using its current EPDCCHconfiguration for monitoring UESS of the second cell.

Another approach to enable EPDCCH monitoring after handover is to allowthe UE to monitor EPDCCH based on a new default EPDCCH configurationafter handover. FIG. 10 shows an example. The UE monitors EPDCCH using adefault EPDCCH configuration of a first cell (default config.) and anadditional EPDCCH configuration (additional config.). The UE maydetermine the default EPDCCH configuration of the first cell implicitlybased on an identifier associated with the first cell. For example, theUE may use signals such as PSS (Primary synchronization signal), SSS(secondary synchronization signal), CRS (cell-specific reference signal)or CSI-RS (CSI reference signal or Channel state information referencesignal) to determine an identifier associated with the first cell.Alternately, the UE may determine the default EPDCCH configuration ofthe first cell based on a field or information element received in a MIB(Master Information Block) or one of the SIBs (System InformationBlocks, e.g. SIB1 or SIB2). The UE may receive the additional EPDCCHconfiguration in a dedicated RRC message (e.g. a“RRCConnectionReconfiguration” message that includes a“radioResourceConfigDedicated” field). The UE receives a handovermessage indicating the UE to handover from the first cell to a secondcell. After receiving the handover message, the UE discontinues EPDCCHmonitoring using the additional EPDCCH configuration and switches toEPDCCH monitoring using a new default EPDCCH configuration associatedwith the second cell. The UE can determine the new default EPDCCHconfiguration of the second cell implicitly based on an identifierassociated with the second cell. Alternately, the UE may determine thedefault EPDCCH configuration of the second cell based on a field orinformation element received in a MIB (Master Information Block) or oneof the SIBs (System Information Blocks, e.g. SIB1 or SIB2) afterreceiving the handover message.

In some implementations, the UE receives a handover message indicatingthe UE to handover from the first cell to a second cell and the UEmonitors EPDCCH using a new default EPDCCH configuration if an EPDCCHconfiguration is not received in the handover message.

In some cases when the UE gets handed over from a first cell to a secondcell, the UE may have to discontinue EPDCCH monitoring and startmonitoring PDCCH. This can happen for example when the second cell doesnot support EPDCCH or has not allocated any resources for EPDCCH. Toenable the UE to quickly start monitoring a control channel afterhandover (either PDCCH or EPDCCH depending on the use case) it isbeneficial to include an indication in the handover message based on orwhich the UE uses to decide which control channel to monitor.

FIG. 11 shows an example. The UE monitors CSS using PDCCH. To determinethe mapping of PDCCH REs the UE uses a first cell ID. The UE alsomonitors UESS using EPDCCH. The UE may determine the mapping of EPDCCHREs using previously determined EPDCCH configuration (e.g., based on adefault EPDCCH configuration and/or additional EPDCCH configuration).The UE receives a handover message indicating the UE to handover fromthe first cell to a second cell. After receiving the handover message,the UE continues to monitor a CSS using PDCCH. However, to determine themapping of PDCCH REs, the UE uses a second cell ID (cell ID of thesecond cell). Within the handover message, the UE receives an indicationbased on which it determines whether to monitor UESS using PDCCH orEPDCCH. The indication can be explicit (e.g. an information element orfield in the handover message). Alternately, the indication can beimplicit. For example, the UE monitors UESS using EPDCCH in the secondcell if a specific field (e.g. EPDCCH configuration field) is present inthe handover message, and it monitors UESS using PDCCH if the specificfield is absent in the handover message. Another example of implicitindication can be if a “transmissionMode” field in the handover messageconfigures the UE to use a first transmission mode (e.g., tm1 or tm2 or. . . tm8), the UE monitors UESS using PDCCH in the second cell, and ifthe field in the handover message configures the UE to use a secondtransmission mode (e.g., tm9) the UE monitors UESS using EPDCCH in thesecond cell.

In another approach, the UE receives a handover message indicating theUE to handover from the first cell to a second cell. After receiving ahandover message, the UE transmits a handover complete message. Thehandover complete message can indicate whether the UE is EPDCCH capable.The UE also transmits a RACH after receiving the handover message (usingthe RACH configuration included in the handover message). Aftertransmitting a RACH, the UE receives a RACH response. The UE determineswhether to monitor EPDCCH based on an indication in the RACH response(e.g. based on the TC-RNTI field).

In some implementations, in order for a new UE (e.g. Rel11 or Rel12 UE)to operate in both a legacy network (i.e., a network that does notsupport EPDCCH) and a “new network” the UE can have two modes. (1) In afirst mode (legacy mode), the UE monitors its CSS/UESS using PDCCH (2)In a second mode (new mode or non-legacy) the UE monitors its CSS/UESSusing EPDCCH

The UE can determine whether to operate in legacy mode or new mode basedon spare bits in MIB (received on a CRS based Physical BroadcastChannel—PBCH), or by looking for a new MIB (received on a DMRS basedEnhanced Physical Broadcast Channel—EPBCH).

In one implementation the UE receives spare bits in a MIB and the spareMIB bits tell the UE to receive a new MIB. The UE determines a defaultEPDCCH configuration using information in either spare bits in the MIBor the new MIB.

In one example, one of the spare MIB bits is set to ‘0’ (or first value)in the legacy network and the bit is set to ‘1’ (or second value) in thenew network. If a new UE reads the ‘0’ value (or first value) for thespecified MIB bit, it monitors PDCCH based CSS/UESS. If the UE reads the‘1’ value (or second value) for the specified MIB bit, it monitorsEPDCCH based CSS/UESS.

In a network that supports both new UEs and legacy UEs, the network hasto distinguish between new UEs and legacy UEs. The network do this byconfiguring the new UEs to use a reserved set of time/frequency/codedomain RACH resources that may be different from (or a subset of) theRACH resources used by the legacy UEs. This configuration informationcan be signalled to the UEs using one or multiple bits of informationtransmitted by an eNB in the network. For instance, the bits may betransmitted as part of MIB (sent on PBCH) or one of the SIBs (sent onPDSCH RBs assigned via CSS PDCCHs whose CRC is scrambled with SI-RNTI).If MIB signaling is used, in one instance, one of the reserved MIB bitsis set to ‘0’ (or first value) in the legacy network and the bit is setto ‘1’ (or second value) in the new network. If a new UE reads the ‘0’value (or first value) for the specified MIB bit, it uses the “defaultRACH resources” for transmitting a RACH. “Default RACH resources” may besame as the resources that Rel8/9/10 UEs use for RACH transmission andthese are typically communicated in a SIB2. If the new UE reads the ‘1’value (or second value) for the specified MIB bit, it uses “new RACHresources” for transmitting a RACH. Information about the “new RACHresources” can be communicated to the UE using an extension to SIB2.Alternately, the UE may determine the new RACH resources usinginformation about the old RACH resources and a predefined mapping rule.The new RACH resources may be a set of RBs that are different from theRBs used by Rel8/9/10 UEs for RACH transmission. Alternately, the newRACH resources may be a set of sub-frames that are different from thesub-frames used by Rel8/9/10 UEs for RACH transmission. Alternately, thenew RACH resources may be a set of code sequences that are differentfrom the code sequences used by Rel8/9/10 UEs for RACH transmission.Alternately, the new RACH resources may be a set of preambles that aredifferent from the preambles used by Rel8/9/10 UEs for RACHtransmission. Alternately, the new RACH resources may be a differentcombination of RB/sub-frame/code-sequence/preamble than theRB/sub-frame/code-sequence/preamble combination used by rel8/9/10 UEs. ARel11 UE that transmits RACH in the new RACH resources can monitorEPDCCH CSS/UESS after receiving TC-RNTI.

Dynamically Determining Whether to Use PDCCH or EPDCCH

In an embodiment of the invention illustrated in FIG. 12, the UE isconfigured with periodic intervals (T1) during which it is required tomonitor both PDCCH and EPDCCH on UESS. During these intervals, the eNBmay schedule the UE using either PDCCH or EPDCCH. However, the blinddecodes are split between PDCCH and EPDCCH (not all aggregation levelscan be used for EPDCCH).

For example, if the UE is scheduled using EPDCCH during T1, it onlymonitors for EPDCCH until the next occurrence of T1. That is, after thefirst EPDCCH based scheduling, UE switches to EPDCCH-only mode andmonitors EPDCCH at all aggregation levels. After receiving ACK (positiveacknowledgement) to first EPDCCH based transmission, network assumes UEhas switched to EPDCCH-only mode. Likewise, if UE is scheduled usingPDCCH during T1, it monitors PDCCH at all aggregation levels until thenext occurrence of T1.

Variations are possible. For example, (1) The duration T1 can be fixed.The mode in T2 could be based on the last control channel received in T1(i.e. switching of modes happens precisely at the end of T1 rather thanwhen UE is first scheduled). (2) If UE is not scheduled during T1, itcan use a default mode during T2 (e.g., PDCCH-only).

It is to be noted that the start of T1 can be aligned with the start ofDRX on duration. This results in having a short window at the start ofeach DRX on duration where the UE monitors for both PDCCH and EPDCCH andsubsequently monitors only one of the two, based on what was used forscheduling in the short window. T2 can include periods where the UE isin active time (i.e., monitoring PDCCH or EPDCCH) and the periods wherethe UE is in DRX (i.e., a low power sleep mode where it is notmonitoring either PDCCH or EPDCCH)

It can be seen from the foregoing that a novel and useful method andsystem for receiving a control channel has been described. It is to benoted that embodiments within the scope of the present disclosure mayalso include computer-readable media for carrying or havingcomputer-executable instructions or data structures stored thereon. Suchcomputer-readable media can be any available media that can be accessedby a general purpose or special purpose computer. By way of example, andnot limitation, such computer-readable media can comprise RAM, ROM,EEPROM, CD-ROM or other optical disk storage, magnetic disk storage orother magnetic storage devices, or any other medium which can be used tocarry or store desired program code means in the form ofcomputer-executable instructions or data structures. When information istransferred or provided over a network or another communicationsconnection (either hardwired, wireless, or combination thereof) to acomputer, the computer properly views the connection as acomputer-readable medium. Thus, any such connection is properly termed acomputer-readable medium. Combinations of the above should also beincluded within the scope of the computer-readable media.

Embodiments may also be practiced in distributed computing environmentswhere tasks are performed by local and remote processing devices thatare linked (either by hardwired links, wireless links, or by acombination thereof) through a communications network.

Computer-executable instructions include, for example, instructions anddata which cause a general purpose computer, special purpose computer,or special purpose processing device to perform a certain function orgroup of functions. Computer-executable instructions also includeprogram modules that are executed by computers in stand-alone or networkenvironments. Generally, program modules include routines, programs,objects, components, and data structures, etc. that perform particulartasks or implement particular abstract data types. Computer-executableinstructions, associated data structures, and program modules representexamples of the program code means for executing steps of the methodsdisclosed herein. The particular sequence of such executableinstructions or associated data structures represents examples ofcorresponding acts for implementing the functions described in suchsteps.

While the present disclosure and the best modes thereof have beendescribed in a manner establishing possession by the inventors andenabling those of ordinary skill to make and use the same, it will beunderstood that there are equivalents to the exemplary embodimentsdisclosed herein and that modifications and variations may be madethereto without departing from the scope and spirit of the disclosure,which are to be limited not by the exemplary embodiments but by theappended claims.

LIST OF ACRONYMS

-   BS Base Station-   CCE Control Channel Element-   CoMP Coordinated Multi-Point-   CP Cyclical Prefix-   CQI Channel Quality Indicator-   CRC Cyclic Redundancy Check-   C-RNTI Cell RNTI-   CQI Channel Quality Information-   CRS Common Reference Signal-   CSI Channel State Information-   CSI-RS Channel State Information Reference Signal-   CSS Common Search Space-   DCI Downlink Control Information-   DL Downlink-   DMRS Demodulation Reference Signal-   eNB Evolved Node B-   EPBCH Enhanced Physical Broadcast Channel-   EPDCCH Enhanced Physical Downlink Control Channel-   EPRE Energy Per Resource Element-   E-UTRA Evolved UTRA-   FFT Fast Fourier Transform-   HARQ Hybrid Automatic Repeat Request-   LTE Long-Term Evolution-   MAC Media Access Control-   MBSFN Multicast-Broadcast Single-   Frequency Network-   MCS Modulation and Coding Schemes-   MIB Master Information Block-   MIMO Multiple-Input Multiple-Output-   MU-MIMO Multi-User MIMO-   OFDMA Orthogonal Frequency Division Multiple Access-   P/S-SCH Primary/Secondary Synchronization Channel-   PBCH Primary Broadcast Control Channel-   PCID Physical Cell Identifier-   PDCCH Physical Downlink Control Channel-   PDCP Packet Data Convergence Protocol-   PDSCH Physical Downlink Shared Channel-   PHICH Physical Hybrid ARQ Channel-   PRB Physical Resource Block-   P-RNTI Paging RNTI-   PSS Primary Synchronization Signal-   QAM Quadrature Amplitude Modulation-   QPSK Quadrature Phase Shift-Keying-   RACH Random Access Channel-   RB Resource Block-   RE Resource Element-   REG Resource Element Group-   RF Radio Frequency-   RNC Radio Network Controller-   RNTI Radio Network Temporary Identifier-   RRC Radio Resource Control-   RRH Remote Radio Head-   RS Reference Signal-   SFN System Frame Number-   SIB System Information Block-   SI-RNTI System Information RNTI-   S-RNTI Serving RNC RNTI-   SSS Secondary Synchronization Signal-   TC-RNTI Temporary Cell RNTI-   tm Transmission Mode-   TP Transmission Point-   UE User Equipment-   UERS UE-specific Reference Symbol-   UESS UE-Specific Search Space-   UL Uplink-   UMTS Universal Mobile Telecommunications System-   U-RNTI UTRAN RNTI-   UTRAN UMTS Terrestrial Radio Access Network

What is claimed is:
 1. A method in a communication device, the methodcomprising: monitoring a first control channel; receiving informationfrom the network regarding a configuration of a second control channel;during a random access procedure between the communication device andthe network: receiving an uplink grant from the network, andtransmitting a message to the network, the message including anindication that the communication device is capable of monitoring asecond control channel; monitoring the second control channel based onthe received configuration information.